Modify external_sst

[laurenchilutti]

Description

FMS 2023.03 contains mixed precision support and had modified the types of sst_ncep and sst_anom to be hard-coded real8 in amip_interp_mod, which would have required updating some code in this repository when we reference sst_ncep and sst_anom in subroutines (such as pmaxmin).
In testing this tag of FMS, we noticed that these variables do not need to come from amip_interp_mod as we allocate them within the dycore. FMS will be updated to no longer declare sst_ncep and sst_anom(see issue: NOAA-GFDL/FMS#1393), and this PR fixes the use statement so that we do not use the amip_interp_mod sst_ncep and sst_anom. We also removed the #ifdef NO_GFDL_SHARED as this is not needed as we will always be compiling the sycore with FMS.

Fixes # (issue)

How Has This Been Tested?

Tested with FMS2023.03 with the SHiELD CI and RTS tests

Checklist:

Please check all whether they apply or not

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[lharris4]

Cleaner is better. Hopefully we can eventually eliminate this routine all together.

[bensonr]

Removal depends on all of the nudging routines that use sst_anom and sst_ncep and the two logical triggers from amip_interp